For the transmission of video signals between consumer electronics video appliances, several interface standards are known. The best video quality can be provided by so-called R, G, B signals, in which the three colors red, green and blue are provided each as separate signals, corresponding to the colors as displayed in a color picture tube. But because this video standard needs three separate signal lines with a high bandwidth for each signal, this standard is rarely used for consumer electronics appliances.
Very common is the CVBS transmission (FBAS in Germany), according to which standard the video signal is comprised of a color signal C and a luminance signal Y, including also a synchronization signal S and a blanking signal B. This video standard is widely used, for example also for terrestrial television transmission. Because luminance and chrominance signals are added together for a transmission via one line, these components have to be separated in a television set for the reproduction on the display.
The CVBS standard has been used since the beginning of color television sets and is a good compromise between picture quality and transmission bandwidth. Because luminance and chrominance signals are closely superposed in this standard, a perfect separation of the luminance and the chrominance signal in a television receiver is not possible and leads for example to cross color and cross luminance distortions. For high quality video recording and video storing therefore often other video standards are used, for example component video signals and S-Video (S-VHS).
The component video standard provides three separate signals, YPrPb, or YCrCb, which provide two color-difference signals Pr and Pb, and the Y signal provides the luminance information, from these three signals all RGB color signals can be generated. The YPrPb signals are similar to the Y, U, V signals as used in a television set, but have different voltage levels. In the S-Video standard, which is used for example as an interface for S-VHS recorders, the color components U and V are combined via quadrature amplitude modulation (QAM) to a chrominance signal C.
Because of a large variety of consumer video appliances, for example VHS and S-VHS recorders, camcorders, DVD-players and DVD-recorders, actual television sets are equipped with several inputs, known for example as AV1, AV2 and AV3, to which each a video appliance can be connected. The video inputs are coupled to an input switching matrix, via which a user of the television set can select a specific input. Because of the various kinds of video standards, the video inputs, or at least the main video input AV1, should be able to handle the video signals of all respective standards. Therefore, a user must know, which video standard is available at the output of the video appliance being coupled to the television set or an automatical recognition of video signal has to be provided by the television set.